The overall goal of this study is to establish a reliable hearing loss induction via surgical tympanic membrane puncture and verification by otoscope visualization and behavioral assessment by clap startle. The purpose of our practical is to develop a model for human hearing conductive disorders. We demonstrate in the practical, the conductive hearing loss surgical procedure, which is a simplification in the malleus removal, the method to verify conductive hearing loss by otoscope visualization, and a simple behavioral clap startle, which validate that conductive hearing loss has occurred.
The main advantage of the procedure we described are non-invasive procedures, verification of conductive hearing loss by otoscope, and validation by clap startle. The present study and procedures were approved by the animal research ethics committee and the City University of Hong Kong, the University of Hong Kong, and the Department of Health of the Hong Kong Special Administrative Region. For the present protocol, we choose rats, but you may choose any rodent.
Weigh animals to ensure proper anesthesia for IP injection. For anesthesia, it is important that animals have the proper dose. Pick up your rat by the scruff.
Ensure your correct dose of ketamine and xylazine for IP injection, and inject. Make sure to perform toe pinch to verify no pain sensation. For surgical setup consists of your anesthetized rat, the microscissors, and your otoscope.
Please thoroughly clean the surgical area with ethanol. Place the surgical drape on the cleaned bench. Subsequently introduce your scissors, otoscope, and rat.
The size of your scissors will depend on the size of your rodent. Under otoscope, visualize the left and right ear of the rat to ensure a healthy tympanic membrane. Grab the helix and extend the external auditory canal to become obscured and blackened.
Here you will introduce the microscissors. Introduce the microscissors to the center of the auditory canal, paying close attention not to nick the tissue. Listen for the pop sound, then twist to ensure displacement of the malleus.
The confirmation of a successful conductive hearing loss surgery, should be made with an otoscope. Evaluate each rat ear before and after surgery with an otoscope with a small diameter speculum. When visualized with an otoscope, the differences between a normal tympanic membrane and a punctured tympanic membrane should be studied.
Here, the normal tympanic membrane on the left has the head of the malleus in place and is drastically different than the punctured tympanic membrane on the right. The punctured tympanic membrane, after the conductive hearing loss surgery, has the malleus displaced and the pars tensa ruptured with the umbo of the malleus and head completely missing. Postoperative care for rodents.
Place the rodent in the home cage under a warm lamp and inject with antibacterial agents and glucose. Corroborate connective hearing loss with behavioral clap startle. The CHL rat is placed next to a normal rat in two adjoining cages.
These are placed in a silent room. Stand half a meter away and clap in equally spaced durations a specific number of times. Here, we choose five.
Here, our representative behavioral results. Note the rat at the bottom does not jump to the loud clap sound. The rat at the top of the screen is startled by these loud clapping sounds.
Please study the before and after the clap difference for these two rats. Failure to induce conductive hearing loss. A failure to induce conductive hearing loss could be caused by bleeding in one or both ears.
And in this case, the rodent should be euthanized. This would indicate that the scissors did not make contact with the tympanic membrane. A no popping sound during the procedure.
A no popping sound would indicate that the conductive hearing loss procedure was poor and not clean. A no popping sound would mean that your microscissors did not make direct contact with the tympanic membrane. Otoscope visualization.
If, when visualizing by otoscope, the tympanic membrane appears normal, this would indicate that no CHL has occurred. A response to the loud clap sound test. This would indicate that no CHL has occurred and the rodent does not have conductive hearing loss.
This would occur when a rat jumps or is startled by a loud clap sound. The main advantage of the procedure we described, are non-invasive procedures, verification of conductive hearing loss by otoscope, and validation by clap startle. After doing the practical, you can induce conductive hearing loss in a rodent model and explore the behavioral and psychophysical manifestations of this hearing disorder.
